Safer Structures
Tuesday, May 8, 2007 at 10:35 Assessing Loads on Silos and Other Bulk Storage Structures: Research Applied to Practice, Em Prof Geoffrey Blight
2006 ISBN: 0415392373, 234 pages, $211
Geoff Blight has spent over 30 years researching and measuring the loads exerted on the walls of structures containing bulk solid materials. This book represents his presentation of the principal outcomes of this work. In the Forward the author acknowledges that since the book deals largely with the results of the research carried out by the author and his colleagues and graduate students, the book contains few references to other work. Readers of the book should bear this in mind as, in some respects, the approaches adopted by Blight vary markedly from what may be regarded as ‘the norm’. For example, Blight dismisses the concept of the ‘switch stress’ saying that it has not been measured in full scale silos, however, his technique for estimating wall loads appears to lack any resemblance to the loads existing in conical hoppers under ‘flow conditions’. It is an estimation of these hopper loads which provide the best basis for predicting the flow (or operational) loads on feeders and gates. The techniques Blight employs for his measurement of relevant bulk materials characteristics reflects his training as a geotechnical engineer and no mention is made of the significant range of alternative techniques and that have been developed and are employed around the world for making these and other more extensive handleability measurements.
A significant proportion of Blight’s work relates to field measurements on full scale structures. This collection of research outcomes is very valuable. Any designer of silo structures should read the book to ensure that they have an appreciation of the possible interactions of the contained bulk solids and the containment structure they are designing. These interactions, which Blight generally refers to as ‘secondary effects,’ are many and variable and in some instances are also very significant in magnitude.
Since in many instances the loads measured by Blight on particular silos were significantly less than the loads estimated by the design codes, Blight is rather critical of the various design codes that exist around the world including the current Australian Standard AS3774-1996 ‘Loads on Bulk Solids Containers’ and the relatively new EN1991-4 ‘Eurocode 1- Actions on Structures, Part 4 – Silos and Tanks’. The significant ‘secondary effects’ discussed (and measured) by Blight provides a very valid reason why design codes, which are trying to cover all eventualities, are often rather conservative in their estimations!
Despite the rather unconventional approaches and conclusions of some of Blight’s research and also the fact that the book only concentrates on the work of Blight and his associates, this book is still very valuable. It highlights the often neglected issues of the interactions of the storage structure and the contained bulk solid. Any designer of bulk solids structures, especially if new to the field, should read this work. However, it is suggested that the book should not convince the reader to regard design codes as being excessively conservative. Instances of storage structures for bulk solids failing catastrophically are still being reported rather regularly!
Review by Em Prof Peter Arnold, Centre for Bulk Solids and Particulate Technologies,
Faculty of Engineering, University of Wollongong.
Assessing Loads on Silos and Other Bulk Storage Structures is available from EA Books, http://www.engineersmedia.com.au/bookshop
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